A New Real-Time Optimization-Based Energy Management Strategy for Battery/Supercapacitor Hybrid Storage System in DC Microgrid

This article presents a new energy management strategy (EMS) for optimal power allocation in the battery/supercapacitor hybrid energy storage (HESS) in DC microgrid applications. The proposed system is composed of a semiactive structure where the supercapacitor is directly connected to DC bus. In this structure, since the main purpose of the HESS is to maintain the DC bus voltage at the desired value, controlling the supercapacitor becomes more important. While, in the semi-active structure, there is no control on the supercapacitor. In this paper, by considering the supercapacitor current as a cost function in the optimization problem, this challenge has been solved. Also, in the case of microgrid excess power mode, a new cost function has been considered to charge the battery with a constant current to reduce the charging time and improve its lifespan. Another objective is to increase battery life by responding the supercapacitor to the sudden power changes and drawing a smooth current from the battery. In order to online determination of the optimal global solution, this multi-objective problem has been converted into a single-objective problem by use of the weighted method and then solved using KKT conditions. Therefore, real-time implementation is the main advantage of the proposed method. Finally, using simulation, the performance of the proposed method is compared with an adaptive cutoff frequency filter-based method and fuzzy logic method, in three 24 seconds different scenarios, in terms of the DC bus voltage regulation, the battery peak current, and the battery state of charge (SoC).